Tutorial quote: apt-p2p is a p2p proxy for apt dowloads, it will act as a proxy between apt requests and a repository server, downloading any request files from peers (if possible), else will fallback to direct HTTP download. In general, apt-p2p save bandwidth, use limited cpu and memory resources and reduce congestion on the ubuntu mirrors.apt-p2p will get the request files from peers, therefore, it will avoid the congestion on the ubuntu mirrors.